raggen in Elof Hellquist, Svensk etymologisk ordbok (1st ed., 1922)
RAGGEN in Johan Ernst Rietz, Svenskt dialektlexikon (1862–1867)
Etymology
At least since 1649, raggen has been used as a name for the devil, the evil one. This is based on an Old Swedish adjective ragher (cowardly, unmanly, bad, heinous), same as Icelandic ragr which also means sexually perverse.
(Any hints on pronunciation? If it is not based on ragg, the emphasis is possibly different, like tomten/tomten.)